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Laboratory evaluation of influence of operational tolerance (acceptance criterion) on performance of hot-mix asphalt concrete.
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  • Abstract:
    The performance of flexible pavements relies heavily on the final quality of the hot-mix asphalt concrete (HMAC) as it

    is produced and placed in the field. To account for production and construction variability while ensuring the quality of the

    HMAC, TxDOT has established a set of relevant operational tolerances, which are incorporated into the 2004 Standard

    Specifications for Construction and Maintenance of Highways, Streets and Bridges. In particular, Items 340/341, 342, 344,

    and 346 provide acceptance criteria for all HMA mixes used by the Department. The operational tolerances for a series of key

    control variables that affect performance are given as a guideline in QC/QA practices. However, the relationship between

    these tolerance levels and mixture performance is not well known. This research project will establish this relationship: how

    do the operational tolerances affect the expected performance of the HMAC? Once this relationship is quantified,

    recommendations will be developed that indicate, if necessary, how the current tolerances should be modified.

    The objective of the study was to determine the effects of variability in key mix design factors, such as asphalt content,

    gradation, and density, on the laboratory performance of different hot-mix asphalt samples that were mixed and compacted in

    the laboratory. Variability was kept within specified limits by the allowable operational tolerances, and performance was

    addressed through the evaluation of the results obtained from volumetric properties and laboratory tests, such as flexural

    fatigue test, Hamburg wheel-tracking test, and overlay tester. A series of statistical analyses were conducted to develop

    relationships between the key mix design factors and the observed laboratory performances of each type of mixture. From the

    analysis, the effects of the main variables on the results of the performance tests used in this study were found.

    Finally, a statistically-based sensitivity analysis was conducted to reveal the relationship between different tolerance

    levels and mixture performance for the individual mixtures types. This research facilitates, for both TxDOT personnel and

    contractors, the evaluation of asphalt mixture performance under different tolerance levels, which will be performance-based

    and supported by a rigorous and sound statistical analysis.

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